A transceiver is a well-known circuit containing a transmitter and a receiver, which are thus capable of transmitting and receiving communication signals, respectively. Conventionally, the transmitter contains a power amplifier (also known as “PA”) that provides the last stage of amplification of the signal to be transmitted.
In most conventional designs, the power amplifier is implemented as a component that is physically separate from other parts of the transmitter and/or transceiver. Power amplifier's made from gallium arsenide (GaAs) or Silicon bipolar junction transistors (SiBJT) are typically used because they have an inherently higher breakdown voltage than transistors made in CMOS circuit, whether the transistors are n-channel or p-channel transistors. While such designs allow for a power amplifier that has the desired amplification,characteristics, they do so at the expense of cost. Not only is a GaAs, SiBJT or other non-CMOS power amplifier costlier than a transistor in a CMOS integrated circuit, but the non-CMOS power amplifier cannot be formed on the same integrated circuit chip as the components of the transmitter and/or transceiver. Both of these factors add to the overall cost of the resulting transceiver.
It has been recognized that it would be beneficial to have a transceiver in which most of the transmitter and receiver circuits are on a single chip, including the power amplifier. For example, in the article entitled A Single Chip CMOS Direct-Conversion Transceiver for 900 MHz Spread Spectrum Digital Cordless Phones by T. Cho etal. that was presented at the 1999 IEEE International Solid State Circuits Conference, there is described a CMOS transceiver chip that includes an integrated power amplifier. This power amplifier is implemented as a three-stage class AB amplifier. While this power amplifier is integrated on the same integrated circuit chip many of the other transceiver components, the power amplifier described has a number of disadvantages.
One of these is that this circuit is not designed to tolerate supply voltages that significantly exceed the transistor breakdown voltages. In particular, transistors used in deep-submicron CMOS circuits having a high-transconductance cannot reliably tolerate junction voltages that are significantly higher than the supply voltage. An integrated RF power amplifier, however, is most efficient when the voltage at the RFout node swings from 0 to at least 2*Vdd, an amplitude made possible by the inductive load at the output of the circuit. The inductive load is typically an inductor connected between the supply and the drain of the output transistors of the power amplifier. Furthermore, since the RFout node is typically connected directly to the antenna, the possibility of transmitted power reflecting backwards to the power amplifier causes the maximum voltage at the RFout node to approach 4*Vdd. This voltage is well beyond the breakdown voltage of modern CMOS devices, and can cause unpredictable performance or device damage.
Another disadvantage is that the integrated power amplifier presented above provides non-linear operation. Further, it is intended for operation in the range of 900 MHz, and not substantially higher frequencies in the gigahertz range.
Still furthermore, when an integrated power amplifier is made on a CMOS chip with a substantial number of the transmitter and receiver components, there is a corresponding increase in the number of pins required. Just adding pins, however, will not necessarily result in a usable circuit. This is because, as the present inventors have found, that there is needed a semiconductor package that provides for dissipation of the thermal energy generated by the power amplifier during operation.
Accordingly, a power amplifier integrated with a CMOS chip that overcomes various ones, and preferably all, of the above disadvantages would be desirable.